The Roman Empire was once so great that it had to be divided into two; thus appeared the Western Roman Empire and later the Eastern -Byzantine-. In the latter, Greek continued to be a common language, and the common word in Greek for “god” is “theos”, which has generated words such as atheist, theocentrism, theist, atheism, etc. In vulgar Romance language, the word Dios is written with a capital letter, because the dominant religion is monotheistic and only one is conceived, but in Latin it is written in lowercase, since it is a common noun, as in Roman religion many gods were considered. On the other hand, the Latin words deus and divus both originate in a common form of archaic Latin, deivos -god- and its feminine form deiva -goddess- which in Classical Latin generate the words dea and diva, and which runs in parallel with ancient Indian and Sanskrit deváh, or for example with Lithuanian devas or Celtic devos. This Indo-European root of variants -dyeu / dyeu- refers to daylight, and to the brightness of light, which in the Indo-European mental background is attributed to the gods; it also provides in Latin the word dies -day: luminous part of the day, characterised by sunlight as opposed to nightand the name of the goddess Diana. In Greek it also gives the word delos -bright, visiblewhich gives rise to the proper name of the Greek island of Delos, appellative -Delio- that the ancient Greeks gave to the god Apollo, and to some modern neologism of Greek base such as the word “psychedelic”, which means “related to the visible manifestation of hidden psychic elements, related to the intense stimulation of psychic powers so that they manifest in visible forms”. Before “god” was pater, that is, God the Father, it was something like an entity of light. Every being of light was a god, and generally it refers to the luminaries in the sky.